This application relates to and incorporates by reference Japanese patent application no. 2001-311679, which was filed on Oct. 9, 2001.
The present invention relates to a controlled compressor apparatus that is preferably used for an air-conditioning system or a refrigeration circuit in a so-called idle-stop vehicle, the engine of which is stopped while the vehicle is temporarily at rest.
For example, known is a conventional controlled compressor apparatus (a hybrid compressor), as disclosed in Japanese Patent Laid-Open Publication No. 2000-229,516, in which an engine or a motor selectively operates a compressor and a refrigeration circuit.
This controlled compressor apparatus operates the compressor via an electromagnetic clutch (by engaging the electromagnetic clutch) while the engine is in operation, whereas, when the engine is at rest, the compressor is driven by a battery-powered motor, with the electromagnetic clutch disengaged.
In this case, control is provided as described below based on the idea that the compressor should operate at a minimum necessary level, since operating the compressor by the motor results in a large amount of power being consumed. That is, the compressor is a swash-plate variable-volume compressor. First, when the discharge volume of the compressor is larger than a predetermined value when it is predicted that the engine will stop, the electromagnetic clutch is turned off after a delay, to further increase the discharge volume. This allows the engine to drive the compressor continuously to lower the cooling temperature. Next, the discharge volume is reduced and the compressor is operated by both the motor and the engine. Thereafter, the electromagnetic clutch is disengaged and the engine is shut down, allowing the compressor to be driven by the motor alone. At this time, the discharge volume is varied according to the required cooling capability.
This arrangement provides reduced power consumption at the time of starting the motor and allows the engine to continuously operate to provide sub-cooling prior to stopping the engine, thereby reducing the power consumption of the motor when the engine is at rest. Furthermore, the discharge volume of the compressor is varied to be consistent with the required cooling capability of the refrigeration circuit, thereby reducing the power consumption of the motor.
However, since the operation of the engine is halted after a delay, to provide sub-cooling prior to stopping the engine, the engine is operated for a longer period of time, which undermines the goal of decreasing fuel consumption.
On the other hand, when the discharge volume is dropped for a lower required cooling capability, the compressor efficiency is reduced accordingly. This makes it impossible to reduce the power consumption of the compressor in proportion to the required cooling capability, and thus the motor consumes more power than should be necessary.
That is, the required cooling capability Q is proportional to the discharge volume V. Generally, in a compressor of a variable-volume type, the rate of effect of various losses (such as a leakage loss at the time of compression or a mechanical loss at the bearings or seals) in the compressor corresponding to the required power consumption L increases as the discharge volume V is dropped. Thus, as shown in FIG. 6, the compressor efficiency xcex7c is decreased.
On the other hand, the actual coefficient of performance (the actual COP) in the refrigeration circuit is expressed as shown by equation 1, and thus the power consumption L of the compressor is expressed by equation 2.
Actual COP=Q/L=xcex7cxc2x7theoretical COPxe2x80x83xe2x80x83Equation 1
L=Q/(xcex7cxc2x7theoretical COP)xe2x80x83xe2x80x83Equation 2
where the theoretical COP is a theoretical coefficient of performance in the refrigeration circuit.
As can be seen from equation 2, the required cooling capability Q and the power consumption L are not proportional to each other due to a drop in compressor efficiency xcex7c. For example, even with the required cooling capability Q being halved (and the discharge volume V also being halved), the power consumption L is not halved due to a corresponding degradation in compressor efficiency xcex7c. It instead becomes larger than it should, thereby causing the motor to consume power unnecessarily by that amount.
In view of the aforementioned problems, an object of the present invention is to provide a controlled compressor apparatus that enables a compressor to provide an increased operating efficiency when driven by a motor alone and thereby reduces power consumption while maintaining an improved fuel efficiency resulting from stopping the engine.
To achieve the aforementioned object, the present invention is essentially a compressor apparatus that is applied to a vehicle having an engine. The engine stopped when the vehicle is at rest while running. The compressor apparatus includes a compressor, which is included in a refrigeration circuit, of a variable volume type for compressing a refrigerant; a motor powered by a battery to operate; and a switching mechanism for switching between the engine or the motor to drive the compressor. The compressor apparatus further includes a controller for selecting either the engine or the motor to drive the compressor and for controlling a discharge volume of the compressor. The controller selectively operates the motor to operate the compressor when the engine is at rest. The controller causes the motor to operate the compressor such that the compressor is turned on or off at a discharge volume of the compressor that is greater, within a variable range, than that continuously required for operating the refrigeration circuit.
This allows the compressor to be operated by means of the motor alone while engine is at rest, which ensures an originally intended idle-stop operation to improve fuel efficiency.
Furthermore, when a low cooling capability is required, the compressor is allowed to operate without reducing the compressor efficiency (xcex7c), which reduces the power consumption of the motor. At this time, the turning on and off operations can eliminate redundant operating time, which reduces the total power consumption.
According to another aspect, the turning on and off operations of the motor are carried out in accordance with any of temperatures at an evaporator included in the refrigeration circuit, at an air inlet through which air cooled down by the evaporator is discharged into a cabin of the vehicle, inside the cabin, and outside the vehicle.
This makes it possible to readily control the turning on and off operations using also a temperature signal provided by a temperature sensor portion that is typically provided in the refrigeration circuit. At this time, it is possible to maintain the minimum required cooling capability to provide cooling while the engine is at rest, reducing the power consumption of the motor.
According to another aspect of the invention, while the engine is operating the compressor, the controller varies the discharge volume of the compressor to be consistent with a discharge volume required for operating the refrigeration circuit.
This makes it possible to make use of the original merits of the compressor of a variable volume type in eliminating shocks, occurring when the discharge volume is varied, to keep a good drive feeling provided while the vehicle is running. That is, while the vehicle is running, the engine drives the compressor regardless of the motor, thereby eliminating the need for worrying about power consumption. In general, high transmission efficiencies are achieved when a drive force is transmitted from the engine to the compressor. Thus, it is much more advantageous to make use of the original merits of the variable volume compressor than to consider the compressor efficiency (xcex7c) of the compressor alone.
According to another aspect of the invention, it is preferable that the compressor is integrated with the motor and is employed as a hybrid compressor selectively driven by either the engine or the motor.